ch01 structure of metals.ppt

Kalpakjian • SchmidManufacturing Engineering and Technology © 2001 Prentice-Hall -1

CHAPTER 1

The Structure of Metals

Kalpakjian • SchmidManufacturing Engineering and Technology © 2001 Prentice-Hall Page 1-2

Chapter 1 Outline

Figure 1.1 An outline of the topics described in Chapter 1


Body-Centered Cubic Crystal Structure

Figure 1.2 The body-centered cubic (bcc) crystal structure: (a) hard-ball model; (b) unit cell; and (c) single crystal with many unit cells. Source: W. G. Moffatt, et al., The Structure and Properties of Materials, Vol. 1, John Wiley & Sons, 1976.


Face-Centered Cubic Crystal Structure

Figure 1.3 The face-centered cubic (fcc) crystal structure: (a) hard-ball model; (b) unit cell; and (c) single crystal with many unit cells. Source: W. G. Moffatt, et al., The Structure and Properties of Materials, Vol. 1, John Wiley & Sons, 1976.


Hexagonal Close-Packed Crystal Structure

Figure 1.4 The hexagonal close-packed (hcp) crystal structure: (a) unit cell; and (b) single crystal with many unit cells. Source: W. G. Moffatt, et al., The Structure and Properties of Materials, Vol. 1, John Wiley & Sons, 1976.


Slip and Twinning

Figure 1.5 Permanent deformation (also called plastic deformation) of a single crystal subjected to a shear stress: (a) structure before deformation; and (b) permanent deformation by slip. The size of the b/a ratio influences the magnitude of the shear stress required to cause slip.

Figure 1.6 (a) Permanent deformation of a single crystal under a tensile load. Note that the slip planes tend to align themselves in the direction of the pulling force. This behavior can be simulated using a deck of cards with a rubber band around them. (b) Twinning in a single crystal in tension.


Slip Lines and Slip Bands

Figure 1.7 Schematic illustration of slip lines and slip bands in a single crystal (grain) subjected to a shear stress. A slip band consists of a number of slip planes. The crystal at the center of the upper illustration is an individual grain surrounded by other grains.


Edge and Screw Dislocations

Figure 1.8 Types of dislocations in a single crystal: (a) edge dislocation; and (b) screw dislocation. Source: (a) After Guy and Hren, Elements of Physical Metallurgy, 1974. (b) L. Van Vlack, Materials for Engineering, 4th ed., 1980.


Defects in a Single-Crystal Lattice

Figure 1.9 Schematic illustration of types of defects in a single-crystal lattice: self-interstitial, vacancy, interstitial, and substitutional.


Movement of an Edge Dislocation

Figure 1.10 Movement of an edge dislocation across the crystal lattice under a shear stress. Dislocations help explain why the actual strength of metals in much lower than that predicted by theory.


SolidificationFigure 1.11 Schematic illustration of the stages during solidification of molten metal; each small square represents a unit cell. (a) Nucleation of crystals at random sites in the molten metal; note that the crystallographic orientation of each site is different. (b) and (c) Growth of crystals as solidification continues. (d) Solidified metal, showing individual grains and grain boundaries; note the different angles at which neighboring grains meet each other. Source: W. Rosenhain.


Grain Sizes

TABLE 1.1ASTM No. Grains/mm2 Grains/mm3

–3–2–10123456789101112

1248163264128256512

1,0242,0484,0968,20016,40032,800

0.72

5.61645128360

1,0202,9008,20023,00065,000185,000520,000

1,500,0004,200,000


Preferred Orientation

Figure 1.12 Plastic deformation of idealized (equiaxed) grains in a specimen subjected to compression (such as occurs in the rolling or forging of metals): (a) before deformation; and (b) after deformation. Note the alignment of grain boundaries along a horizontal direction; this effect is known as preferred orientation.


Anisotropy

Figure 1.13 (a) Schematic illustration of a crack in sheet metal that has been subjected to bulging (caused by, for example, pushing a steel ball against the sheet). Note the orientation of the crack with respect to the rolling direction of the sheet; this sheet is anisotropic. (b) Aluminum sheet with a crack (vertical dark line at the center) developed in a bulge test; the rolling direction of the sheet was vertical. Source: J.S. Kallend, Illinois Institute of Technology.

(b)


Annealing

Figure 1.14 Schematic illustration of the effects of recovery, recrystallization, and grain growth on mechanical properties and on the shape and size of grains. Note the formation of small new grains during recrystallization. Source: G. Sachs.


Temperature Ranges for Various Processes

TABLE 1.2Process T/TmCold workingWarm workingHot working

< 0.30.3 to 0.5> 0.6

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